The well known 35 mm roll film is encased in a magazine and sold on market in that form. The encased 35 mm roll film is as such charged into a camera and exposed to light for every shooting. The encased 35 mm roll film is then taken out of the camera and processed in a darkroom to produce photographic images. Thus, the 35 mm roll film is highly protected from unintentional exposure to light in a magazine.
In contrast, a Brownie film of 120 size of 220 size is not encased in a magazine and is protected from exposure to light by a combination of a pair of light-shielding flanges equipped at both ends of a spool and a light-shielding backing or leader paper, respectively.
A typical structure of the photographic 120-size Brownie film roll is illustrated in FIG. 1 in an extended form. A typical photographic 120-size film roll comprises a spool 13 which has a spool core 14 having a slit therein and a flange 15 at both ends of the spool core 14 and a photographic film 12 which is placed and fixed by an adhesive tape 21 on a continuous light-shielding backing paper 11 in which one end of the backing paper 11 is inserted into the slit of the spool core 14 and other portion of the backing paper 11 is would on the spool core 14 to form multiple convolutions. The outermost convolution of the backing paper 11 is fixed on its preceding convolution by a sealing tape 111a so that the photographic film 12 can be protected from exposure to light.
Although the photographic 120-size film is protected from exposure to light by a combination of a pair of the flanges and the light-shielding backing paper, it is liable to be exposed to light in its side area. The light sometimes enters through an unintentionally produced space or clearance between a side edge of the backing paper and a periphery of the flange to expose the side area of the photographic film.
In order to avoid the unintentional exposure of photographic film, the known backing paper is produced to have a width equal to or slightly larger than the distance between the two flanges of the spool. However, the use of a light-shielding backing paper having a width equal to or slightly larger than the distance between the two flanges sometimes disturbs smooth winding due to possible friction produced between the side edge of the backing paper and the inner surface of the flange. In that case, the photographic film roll wound on the spool core likely has a diameter or a height larger than the diameter or height of the flange. Thus formed photographic film roll is easily exposed to light when it is not placed within a light-shielding bag or a camera.
Japanese patent Provisional Publication No. H4-136842 describes a photographic film roll using a light-shielding backing paper which has a width (L.sub.1) satisfying the condition of (L.sub.1 -L.sub.2)/L.sub.1 =-1% -0.3% at 23.degree. C., 50% RH [L.sub.2 is a distance between the two flanges] and which has one or two skived thinner side portions. The backing paper is adjusted to have a water content of 3 wt. % or less, wound on a spool, and made to have a water content of 4 to 9 wt. %. According to the description of the Publication, the backing paper has an increased width upon having the increased water content so that the side edges of the backing paper are brought into close contact with the inner surfaces of the flanges. Moreover, the skived side portion of the backing paper becomes more flexible to enable more close contact with the inner surface of the flange. For these reasons, a continuous photographic film is tightly wound on a spool and thus produced photographic film roll is highly protected from exposure to light. It seems that the disclosed photographic film roll is economically disadvantageous because an additional step for skiving the side portion(s) of the backing paper should be included in the preparation of the photographic film roll.
Japanese Patent Provisional Publication No. H9-288335 describes a photographic film roll in which a depression in the form of a ring is formed in a flange surface and a backing paper is adjusted to have a width larger than the distance between the two flanges by 50 to 100 .mu.m. It is described that the wider backing paper is effective to keep the photographic film from exposure to light and the depressed flange assists smooth winding of the backing paper.